Epidemiology and Physiology of Pain

Epidemiology of Pain

• Pain is a protective mechanism
• It's the most common symptom prompting medical treatment
• Effective pain management leads to quicker recovery, better function, and fewer postoperative complications

Pain: Ascending Signals Overview

• Nociceptors are pain receptors
• A-delta fibers are large and myelinated
• C fibers are smaller and unmyelinated
• The spinothalamic tract is an ascending pathway that carries pain signals to the brain
• The brain interprets and perceives these signals

Pain: Descending Signal Overview

• The brain interprets incoming pain signals and sends outgoing signals
• Endogenous opioids (endorphins, enkephalins, dynorphins) are natural analgesic neurochemicals
• Opioids bind to pain receptors, blocking signaling from pain fibers

Simple Reflex Arc

• Protective responses that do not involve brain input are simple reflex arcs
• An example is the patellar reflex
• Afferent neurons carry incoming signals to the dorsal horn of the spinal cord
• Interneurons connect afferent and efferent neurons
• Efferent neurons transmit outgoing signals from the anterior spinal cord to muscles

Spinal Cord-Brain Connection

• The brain interprets pain signals
• Signals travel to and from the brain via pathways
• The spinothalamic tract is a primary ascending tract for pain signals
• The corticospinal tract transmits outgoing signals from the brain

Neurotransmitters and Pain

• More than 50 neurotransmitters are involved in pain signal transmission, either exciting or inhibiting it
• Pharmacological manipulation of neurotransmitters is used in pain management, including medications that increase levels of serotonin to treat migraines

Neurochemicals and Their Action

• Prostaglandins enhance inflammation, pain, and edema (from COX-1 pathway)
• Interleukins enhance inflammation and pain
• Tumor necrosis factor enhances inflammation, edema, and decreases appetite
• Leukotrienes enhance inflammation, edema, and bronchospasms
• Bradykinins enhance inflammation
• Glutamate amplifies pain signals
• Substance P amplifies pain signals
• Enkephalins and endorphins provide inhibitory influences on pain signals
• Acetylcholine, GABA, norepinephrine, dopamine, and serotonin have inhibitory actions on pain in the spinal cord and brain
• Serotonin conveys analgesic signals from the PAG area to the NRM of the brain, decreasing in migraines

Gate Control Theory of Pain

• Pain signals travel to and from the brain
• Pain is not always proportional to the injury
• Phantom pain is not adequately explained by gate control theory
• Large-diameter nerve fibers (e.g., sensory) modulate pain signals
• Small-diameter pain fibers transmit pain signals
• Interneurons act like a "gate" to regulate pain signal transmission

Steps of Gate Control Theory

• Transduction: Painful stimuli are converted into neuronal signals
• Transmission: The neuronal signal travels along nerves
• Modulation: Other neurons influence the pain signal, including a "gate"
• Perception: Conscious awareness of the pain

Neuromatrix Pain Theory

• Explains phantom pain
• The body-self neuromatrix is located in the brain
• Pain originates from nerve impulses in the neuromatrix
• The neuromatrix develops from sensory input throughout a person's life
• The brain can generate pain signals independently of nociceptive stimulation

Types of Pain

• Acute pain lasts hours or days and resolves with healing
• Chronic pain lasts beyond the expected healing time, can be caused by persistent inflammation, and doesn't serve a biological or protective function
• Neuropathic pain is caused by injury or malfunction of the nervous tissue, characterized by burning, tingling, and numbness

Sources of Pain

• Cutaneous pain originates from the skin
• Deep somatic pain arises from ligaments, tendons, and other deep tissue structures in poorly localized areas
• Visceral pain comes from deep organs
• Referred pain occurs at a distance from the actual site of pathology
• Phantom pain is felt in a limb that has been amputated

Pain Assessment

• Pain is a subjective 5th vital sign
• Variability in pain experiences exists among patients
• Nonverbal and verbal expressions of pain may vary
• Distinguishing features of pain can aid in diagnosis & identification of causes (e.g., peripheral artery disease)

OLD CART Pain Assessment

• Onset: When did the pain begin?
• Location: Where does it hurt?
• Duration: How long does it last?
• Characteristics: What does it feel like?
• Aggravating factors: What makes it worse?
• Relieving factors: What makes it better?
• Treatment: What treatment has been tried, and what effect did it have?

Visual Analog Scale

• A visual scale used to measure pain intensity
• A patient rates their perceived pain level on a scale ranging from no pain to worst imaginable

Pediatric Pain Scales

• Neonatal Infant Pain Scale (NIPS)
• Faces, Legs, Activity, Cry, Consolability (FLACC) scale
• Premature Infant Pain Profile (PIPP-R)
• Wong-Baker FACES Pain Scale
• Bieri-Modified scale
• COMFORT scale

Pediatric Pain Assessment

• Characteristics of facial responses to pain in infants (e.g., bulging brows, clenched jaws, and crying) are observed.

Geriatric Considerations

• There is a tendency to undertreat pain in older adults, especially those with dementia

Dementia Patients and Pain Assessment

• Using pain assessment scales (e.g., PAINAD) for patients with dementia is important.

Diagnosis of Pain

• Assessing pain severity using a reliable scale
• Other diagnostic tools include: blood tests, nerve conduction studies, electromyography, nerve injections, and imaging tools

Treatment: WHO Step Analgesic Ladder

• If multiple pain relievers are being used, their mechanisms of action should differ
• The WHO analgesic ladder is used in a bidirectional fashion
• Step 1: Mild/moderate pain — Nonopioid analgesics
• Step 2: Moderate/severe pain — Mild opioids
• Step 3: Severe pain — Strong opioids + adjuvants

Treatment: Modified WHO Analgesic Ladder

• Includes non-pharmacological methods like acupuncture, massage, TENS, and exercises
• Different pain levels and appropriate interventions on the ladder tailored in a similar bidirectional fashion

Nursing Interventions for Pain Management

• Monitoring vital signs
• Effective communication with patients
• Proper body positioning
• Using healing touch
• Patient education regarding pain management

Three Major Classes of Pharmacological Pain Relievers

• Opioids
• Nonopioids
• Adjuvants

Opioids (Pain Relievers)

• Considered a controlled substance
• Morphine is a prototypical opioid
• Produces analgesia, euphoria, and sedation
• Most effective given before pain onset
• Can cause respiratory depression, constipation, nausea, dizziness, and physical dependence

Complications of Opioid Use

• Substance abuse
• Addiction
• Tolerance
• Withdrawal
• Buprenorphine can be used to wean patients off opioids
• Naloxone can reverse opioid overdose effects

Nonopioid Analgesics

• Acetaminophen (Tylenol)
• NSAIDs (aspirin, ibuprofen, naproxen, celecoxib)
• Block prostaglandin synthesis by inhibiting COX enzymes
• COX-1 inhibition affects stomach, platelets, GI mucosa
• COX-2 inhibition effects inflammation and pain
• Celecoxib targets COX-2 selectively

Adjuvant Medications

• Antidepressants
• Local anesthetics
• Peripheral nerve blockade
• Injected corticosteroids
• Anticonvulsants
• Topical pain relievers
• Cannabinoids

Nonpharmacological Pain Management

• Nursing interventions
• Physiotherapy
• Occupational therapy
• Acupuncture
• Transcutaneous electrical nerve stimulation (TENS)
• Peripheral nerve cryoanalgesia
• Guided imagery
• Intradiscal electrochemical therapy
• Virtual reality
• Ultrasound-guided peripheral nerve stimulation
• Botulinum neurotoxin
• Psychological counseling

This quiz explores the fundamentals of pain, including its role as a protective mechanism and the different pathways involved in pain signaling. Understand the concepts of nociceptors, reflex arcs, and the body’s natural pain management strategies. Perfect for students studying pain management and physiology.